Don't send the LE Set Privacy Mode command if it's not supported

LE Set Privacy Mode is currently guarded by LE Privacy feature, which is
enabled on some 4.x controllers, that don't support LE Set Privcay Mode
that was added in 5.0 spec.

Bug: 62809491
Test: Turn Bluetooth on/off with Angler (4.x) and check for 
      Set Privacy Mode
Change-Id: Ie9a164d98558db2e1fe76d90eb6ab93e4cec89d0